The purpose of the proposed study is to develop a method for highly selective injury to pain sensitive neurons within the DRG. Phase I results showed a positive accumulation of a photocytotoxic dye encapsulated in latex nanosphere particles in the DRG. Pulsed and CW laser radiation effected selective, dose-dependent injury to small diameter neurons in the absence of non-specific injury to all control groups. The experiments successfully completed in Phase I will be refined and expanded in mice and rats to confirm histologically and optimize the choice of laser parameters. Sensory and motor neurophysiologic effects will be investigated in larger animals using behavioral assessment and sophisticated near-nerve potential and microneurography techniques. A prototype laser/fiber optic delivery system will be developed and refined for this application. The intent in Phase II is to set the stage for pre-clinical investigations in primates and clinical trials in Phase III. This technology would offer a therapy for intractable pain syndromes associated with malignancy, metabolic neuropathies, and peripheral nervous system trauma.